Geoscience Reference
In-Depth Information
The dominant factor behind water problems, however,
has been the continual intensification and change of
agriculture from the traditional dry farming system of
cereals, olives and livestock to commercial systems for
vegetables and orchard fruits, particularly citrus and
avocados. These new crops require irrigation. Agricultural
technology has responded by building more reservoirs and
using more and more powerful water pumps - from hand,
through animal to diesel and electrically driven pumps;
this technology has enabled water to be obtained from
depths in excess of 400 m. Deeper and deeper wells are
required to keep pace with declining water levels, and
there is increasingly a problem with the quality of this
deeper water.
The two reasons for this situation are climate and
anthropogenic influence. Mediterranean regions were cool
and dry in glacial times (
c
. 15 ka
BP
), treeless steppe being
characteristic. Temperatures ameliorated in the Holocene
to reach a maximum some 5 ka
BP
. A continuous forest
cover of evergreen and deciduous trees had established
itself by then.
The Mediterranean landscape is like a palimpsest;
it shows the remains of successive human societies
superimposed on the landscape and on one another.
Those societies, in the Mediterranean region itself, have
had successive impacts on the natural landscape from
Neolithic settlement, Bronze Age people, Phoenicians,
Greeks, Romans and Moors. Modern pressures have
continued, with agricultural intensification, irrigation and
all the trappings of tourism. Tourist villages and golf
courses now exist side by side with irrigated citrus
plantations and horticulture under polythene sheeting.
Increasingly the natural vegetation and soils are restricted,
just as in Britain, to inaccessible 'islands' and unwanted
rocky hillsides.
CONCLUSION
The present ecosystems of Mediterranean regions can be
regarded as the degraded remnants of a biome which was
once dominated by mixed evergreen and deciduous forest.
KEY POINTS
1
Mediterranean ecosystems are dominated by the seasonality of the Mediterranean climate. Plants and
animals have devised many strategies to adapt to, and survive in, the hot, dry summer. Production and
reproduction take place during the more humid and cooler period from autumn to spring. This is the time
when most weathering, geomorphological processes and soil-forming processes are operative too.
2
Despite the overriding importance of climate, there are variations in vegetation and soil according to
regional and local factors. A zonation of ecosystems is found with increasing altitude. There is also a very
powerful effect of aspect due to different annual radiation budgets on north- and south-facing slopes. There
is also a change in vegetation from valley side to valley floor, related to moisture availability.
3
The final set of controls on Mediterranean ecosystems is the many human pressures - hunting, grazing,
deforestation, fire and cultivation. The net result of these pressures over millennia has been to reduce the
extent of the natural Mediterranean evergreen forest. Many of the shrubby and steppe-like vegetation
communities we see today have been degraded from the forest, but equally some are themselves natural
under the stressful environmental conditions. Soil erosion has been accelerated, making the depth of soil
another key factor influencing vegetation. There are often big contrasts between the rocky outcrops and
thin soils of ridges and upper slopes and the deeper soils of valleys and depressions.
